The present invention relates to the preparation of olefin oxides and in particular relates to new catalysts for use in the process of autoxidation of ethylenically unsaturated organic compounds to the corresponding oxirane compounds.
A number of catalysts have been employed in the liquid phase oxidation of ethylenically unsaturated organic compounds. U.S. Pat. No. 3,259,638 shows the use of compounds of Groups IV-A, V-A or VI-A of the Periodic Table excluding chromium. Selectivity for the epoxide with each catalyst was less than 50%. The major by-products were epoxy-alcohols. The general disadvantages of the prior methods, particularly the catalysts employed in such autoxidations were long reaction times, low conversions and low selectivity to the epoxide, i.e., usually less than 50%. The term autoxidation is understood to mean the reaction of a substance with molecular oxygen without the intervention of a flame. In addition to the epoxide a number of by-products are possible from the autoxidation of olefins, e.g., epoxy-alcohols, diols, olefin hydroperoxides, aldehydes, ketones, water and carbon dioxide. If the desired product is the epoxide then the production of such by-products and the necessity of separating them from the epoxide can make the process economically unattractive. The by-products are often quite useful, e.g., acetone is a common product and the uses of acetone are well known, however, acetone is a far less valuable material than many of the common or desirable olefinic starting materials.
It is an object of this invention to provide an improved process for the autoxidation of ethylenically unsaturated organic compounds. It is a further object of this invention to provide a process which has high selectivity for epoxides. These and other objects will become apparent from the discussion below.